Passive optical networks are widely used, for example in Fiber To The Premises (FTTP) service or a Fiber To The Curb (FTTC) services. Since the PON uses passive devices, power supply is not required for managing the optical devices except the end points equipment. Furthermore, the PON can provide high-speed data services over a relatively large service area.
Examples of the PON include an Ethernet-passive optical network (E-PON) using a time division multiplexing (TDM) communication scheme. The E-PON is an Ethernet based PON used for point-to-multipoint connections, and the Institute of Electrical and Electronics Engineers (IEEE) 802.3ah provides complete standards for the E-PON. In the E-PON, a passive splitter of a Remote Node (RN) splits an optical core of a service provider so as to distribute the optical core to subscribers, and a passive optical coupler of the RN couples optical cores of subscribers together so as to transmit data from the optical cores of the subscribers to the optical core of the service provider. Therefore, downstream data from the service provider are naturally broadcasted.
In another type of the PON called wavelength division multiplexing-passive optical network (WDM-PON), the wavelength of an optical source is used. In the WDM-PON, pluralities of wavelengths are multiplexed.
As communication volume increases, there is a need for an optical network that can efficiently accommodate increasing subscribers and/or communication volume without wasting network resources. Specifically, it is advantageous to be able to upgrade existing PON system to provide higher performance without replacing the entire fibers spans.
U.S. Pat. No. 6,344,919; to Dutta, et al. entitled “Methods and systems for producing linear polarization states of light at the end of a length of optical fiber”; filed May 5, 2000; discloses methods and devices for quickly producing all possible linear polarization states of light at the output of a length of optical fiber. Linearly polarized light is input and is transmitted through a fiber. Due to the birefringence of the fiber, light at the output of the fiber is elliptically polarized irrespective of the input polarization. The elliptically polarized states of light at the output are generated as an arbitrary circle on an output Poincare sphere. This arbitrary circle is then manipulated to produce a final circle substantially coinciding with the equator of the Poincare sphere. This final circle represents all possible linear polarization states at the output of the fiber. The disclosed device eliminates the need for determining transformation matrices and performing point-by-point calculations in order to obtain input polarization settings for polarization-based, passive optical network (“PON”) testing.